Method for initiating in situ combustion with pyrophoric materials



well.

United States Patent Ofitice 3,1791%? Patented Apr. 20,1Q65

3,179,169 METHUD FOR INITIATING IN SITU C'OMBUS- TIUN WITH PYROPHQRIC MATERIALS Carl A. Cline and Louis David Trapnell, Ponca City, Okla, assignors to Continental Uil Company, Ponca (Iity, Okla, a corporation of Delaware No Drawing. Filed Oct. 20, 1960, Sier. No. 63,722 4 Ciaims. (Ql. 166-38) This invention relates to a method for igniting subterranean hydrocarbon-bearing reservoirs in conducting recovery operations generally known as in situ combustion recovery. The in situ combustion of such'reservoirs is a well known method for the secondary recovery of hydrocarbons, and this invention is particularly directed to the initiation of such subterranean combustion.

This technique of secondary production of hydrocarbons comprises the initiation of combustion in the carbonaceous strata of the reservoir and the resulting propaagation of the combustion zone through the reservoir by either a direct orinverse oxygen-containing gas drive whereby the heat of combustion of a portion of the by drocarbons displaces the remainder of the hydrocarbons in the reservoir to adjacent recovery wells.

A conventional method of in situ combustion recovery entails initiating combustion in the subterranean reservoir surrounding a well bore designated as the ignition well, whereaiter the combustion front is directed toward sur- 'rounding recovery well bores traversing the reservoir.

ery is the initiation of combustion in the reservoir ad-' jacent the ignition Well. The basic mechanism of transferring the. necessary heat required for continued combustion of a self-sustaining nature comprises injecting oxygen containing gas through a heated portion of the T reservoir adjacent the ignition well wherein combustion has been previously initiated. Various methods have been utilized to heat the reservoir to initiate combustion therein and to achieve the temperatures necessary for continuous self-sustaining combustion. These methods include utilizing downhole heaters of either an electrical or gas burner construction, injecting heated gases from the surface, injecting highly reactive chemicals such as halogens to react with the hydrocarbons of the formation, and injecting high energy fuels such as hydrazine along with strong oxidizing agents. The foregoing methods wherein a heating device is utilized require the insertion of a downhole heater into the well bore whereafter air is passed by the heater in order toelevate the temperature in the reservoir surrounding the ignition These heaters are complicated and expensive and the results are often other than satisfactory either due to fthe fact that the heat is not applied to the formation at the desired depth or the heat is undesirably concentrated at some particular location causing the heater or supporting cable to become subject to excess temperatures with a malfunction and loss of the heater prior to sufliciently initiating of combustion. The use of chemicals which produce heat by exothermic reaction with hydrocarbons has the inherent disadvantage of being subject to inadvertent reaction prematurely with the hydrocarbons presentwithin the well bore at other than the desired location. The use of certain of the foregoing chemicals requires the inclusion of catalysts or inhibitors in order to control the rate of reactivity and heat produced therefrom in order to avoid the undesirable fusing air or other oxygen-containing gas.

of root; or establishment of water blocks within the reservoir.

It is an object of the present invention to provide an improved method for initiating combustion in subterranean hydrocarbon-bearing reservoirs in order to esablish in situ combustion therein.

Another object of the present invention isto provide an improved method of initiating in situ combustion whereby the application of heat to the reservoir is controlled both as to the amount and the location of application within the reservoir.

A further object of the present invention is to provide an improved method for initiating in situ combustion which is dependable, efiicient and avoids the necessity of using complex equipment or ignition means within the well bore.

Other objects and advantages of the present invention will be apparent from the consideration of the following disclosure of invention. V

In brief, the present invention is broadly directed to the initiation of in situ combustion by introducing a hydrocarbon-miscible pyrophoric substance into a subterranean reservoir followed by the injection of an oxygencontaining gas until the initiation of combustion is accomplished. p

The initiation of in situ combustion in a subterranean reservoir containing hydrocarbons and being traversed by a plurality of well bores, one of which is an ignition well, as taught by the present inventionis very simple and requires the utilization of substantially no downhole equipment. In general, any substantially hydrocarbonsoluble pyrophoric substances are suitable, with the preferred substances suitable for use in the present method being the oxidizable lower alkyl derivatives of boroh, aluminum and zinc which are soluble in petroleum hydrocarbons. More specifically, the preferredsubstances include compounds having the following structures:

(R B; R R R Al; R R Zn in which R is hydrogen or an alkyl group having from 1 to about3 carbon atoms, R R R and R are alkyl groups having from 1 to about 4 carbon atoms. Examples of suitable substances with their boiling points are listed below; t

Generally speaking, these substances produce in the neighborhood of 100,060 B.t.u. per gallon by combustion at atmospheric pressure, for example the heats of combustion of triethylaluminum and triethylborinc are 127,-

700 B.t.u./gal. and 116,500 Btu/gal. respectively. As

a consequence of. the formation of combustion products of low specific heat, the effective combustion temperatures of thesesubstances are also quite high.

In the operation of the method of the present invention, the pyrophoric substance is mixed with a suitable hydrocarbon, preferably one having a relatively low viscosity, such as kerosene, pale oil, or diesel fuel, in a container suitably adapted to preclude any contact with The proportions of the solution are adaptable to individual formations in that one possible method of controlling the rate of heat production within the formation is to control the ratio of pyrophoric substance to hydrocarbon. By the inclusion of a lesser amount of pyrophoric substance in the solution there is achieved a reduced concentration of the heat produced during the subsequent stage of initiating the in situ combustion, and the converse of the foregoing occurs when greater proportions of the pyrophoric substance are included in the solution. From the foregoing table it is evident that at least one of the suitable pyrophoric substances is a gas at normal conditions so it becomes possible to obtain homogeneous vapor phase mixture containing those substances, or they may be placed in a solution with liquid hydrocarbons after requisite conditions of pressure and temperature are met; The remaining pyrophoric substances are normally liquid and can be handled in solutions in hydrocarbons at atmospheric pressure by taking the normal precautions necessary with a highly combustible liquid.

Subsequent to the preparation of the fluid solution as specified above it is necessary that the solution be displaced into the subterranean reservoir surrounding the well bore of the ignition well. This step may be accomplished in any one of several methods which are conventional in the art. The mixture may be placed in the well bore adjacent to the subterranean reservoir by means of injecting it through a line in communication with the surface, or the solution may be placed in a suitable container and lowered into the well bore to a predetermined depth whereafter the solution is released from the container by a mechanical valve arrangement or by rupturing the container, providing it is of a sufiiciently frangible nature. Prior to the placement of the pyrophoric solution in the well bore the bore should be evacuated of any oxygen-containing gas which may be accomplished in many ways, such as by merely injecting a volume of hydrocarbon into the well bore to form a blanket separating the solution from contact with the atmosphere or other oxygen-containing gases within the well bore.

Thereafter the pyrophoric fluid mixture is displaced into the reservoir adjacent the well bore by means of further injection of hydrocarbons, either gaseous or liquid, depending upon the nature of the pyrophoric mixture, so that pressure will be applied to the mixture causing it to be displaced into the formation. The placement of a specified amount of the pyrophoric fiuid in the well bore is most readily accomplished by utilizing a container lowered into the Well bore whereafter the specific volume is displaced in the reservoir to the desired distance. In the event that larger volumes of the pyrophoric solution are required to furnish the necessary heat, it is more advantageous to inject the solution through a surface line wherein greater volumes of the pyrophoric substance may be introduced, or the same volume in conjunction with greater amounts of hydrocarbons may be introduced. The displacement of the pyrophoric fluid into the reservoir may be controlled in order that the mixture may be placed at any predetermined distance from the ignition well bore, enabling the heat of combustion to be applied to the reservoir formation at the most desirable location.

The final step of the present invention is the injection of an oxygen-containing gas, such as air or elemental oxygen, into the reservoir wherein the pyrophoric substance has been previously displaced. Upon contacting the pyrophoric fluid the oxygen causes an immediate oxidization reaction to occur whereby peroxy compounds, carbon dioxide and minute quantities of water and metal oxides are formed, together with the release of great quantities of heat. Following the initial oxidization reaction, the rate of oxygen consumption and heat generation increase rapidly, probably promoted by the presence of the peroxy compounds, until the temperature within the formation has been raised to the combustion point of the hydrocarbons contained therein, usually in the range of 500 to 700 F. The method of the present invention is complete upon the production of sufiicient heat by the pyrophoric substance to establish self-perpetuating combustion of the hydrocarbons within the reservoir. Thereafter the secondary recovery method of in situ combustion may be carried forward by merely continuing the injection of an oxygen-containing gas, whereby the hydrocarbons of the formation provide the fuel to establish and propagate the combustion throughout the reservoir.

The pyrophoric substances disclosed herein as being operable may be utilized separately, or it is possible to combine two or more of them into a mixture in order to take advantage of some of the individual characteristics of several, such as economics, availability, speed of reaction, etc. This method of initiating in situ combustion in the formation surrounding the well bore is particularly applicable when preheating the formation prior to the injection of water or other displacement fluids. It is also utilizable as a means for providing heat in a well work over situation, such as the removal of parafiin, or generally in any instance where there is a need for heat stimulation.

The present method of heat generation may also be utilized in conjunction with a fracturing operation, wherein the pyrophoric substance is injected into the formation prior to fracturing, subsequent to the establishment of the fracture in the formation, or as the fracturing fluid to which the hydraulic and hydrostatic pressure for accomplishing the pressure are actually applied. This will result in the substance being placed in the vertical or horizontal fractures about a well bore and provide a more porous media wherein the combustion can be initiated. The utilization of a fracturing technique in conjunction with initiating combustion as disclosed herein will be particularly advantageous when the porosity of the formation is limited due to the fact that there are often combustion products formed which will plug a normally satisfactorily flowing reservoir. Certain other modifications in the foregoing disclosure of the invention will be apparent to those skilled in the art and the specific embodiments disclosed are not to be construed as imposing limitations upon the scope of the present inventive method.

In order to disclose more clearly the nature of the present invention, the following specific embodiments are furnished to illustrate the herein described method. As an example, the method of the invention is applied to a subterranean reservoir containing crude oil of a viscosity of about 500 centipoises in a formation at a depth of 1015-1035 feet having a porosity of 25 percent and a temperature of F Analysis of cores indicates combustion is developed at about 600 F, and that 33 B.t.u. of heat are required to raise the temperature of a cubic foot of the formation each degree Fahrenheit.

An injection of about 205 gallons of triethylaluminum into the 20 feet of formation is suflicient to provide 26 million B.t.u. of heat whereby the initiation of combustion within the reservoir to the extent necessary to allow development of in situ combustion is accomplished.

The invention having been thus described, whatis claimed and desired to be secured by Letters Patent is:

l. A method for initiating in situ combustion in a subterranean hydrocarbon-bearing reservoir traversed by a well bore which comprises introducing into said well bore a hydrocarbon-soluble substance selected from the class of compounds having the structures (R R R R Al, and R R Zn in which R is hydrogen or an alkyl group having from 1 to about 3 carbon atoms, and R R R and R are alkyl groups having from 1 to about 4 carbon atoms, displacing said substance into said reservoir, and injecting an oxygen-containing gas through said well bore into said reservoir such that said substance can be immediately contacted by subsequently injected oxygen-containing gas to initiate oxidation and oxidizing said substance with oxygen-containing gas to produce heat sulficient to ignite hydrocarbons present Within said reservoir.

2. The method of claim 1 in which the hydrocarbon: soluble substance is triethylborine.

5 i 6 3. The method of claim 1 in which the hydrocarbon- 2,935,839 Beatty et al May 19, 1960 soluble substance is triethylalurninum. 3,057,763 Hunt et a1. Oct. 9, 1962 4. The method of claim 1 in which the hydrocarbon soluble substance is diethylzine. OTHER REFERENCES 5 Jet Propulsion Boosts Interest in Flame Mechanics, References Cited the file of thls patent Chemical and Engineering News, vol. 26, No. 39, Septem- UNITED STATES PATENTS ber 27, 1948, pages 2892-2893. 2,747,672 Simm May291956 The Gallery Chemical (30., Gallery Compounds To 2,863,510 Tadema et a1 Dec 9, 1953 Lead You to New or Improved Products, Chemical and 2, 30,302 carpenter 7 1959 10 Efiginefiring NfiWS, M y 1959, Pages UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,l79,l69 April 20, 1965 Carl A. Cline et al.,

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as correc ted below Column 4 line 63, for "(R read (R B Signed and sealed this 28th day of September 1965.,

(SEAL) Atlest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A METHOD FOR INITIATING IN SITU COMBUSTION IN A SUBTERRANEAN HYDROCARBON-BEARING RESERVOIR TRAVERSED BY A WELL BORE WHICH COMPRISES INTRODUCING INTO SAID WELL BORE A HYDROCARBON-SOLUBLE SUBSTANCE SELECTED FROM THE CLASS OF COMPOUNDS HAVING THE STRUCTURES (R1)3, R1R2R3AL, AND R4R5ZN IN WHICH R1 IS HYDROGEN OR AN ALKYL GROUP HAVING FROM 1 TO ABOUT 3 CARBONATOMS, AND R2, R3, R4 AND R5 ARE ALKYL GROUPS HAVING FROM 1 TO ABOUT 4 CARBON ATOMS, DISPLACING SAID SUBSTANCE INTO SAID RESERVOIR, AND INJECTING AN OXYGEN-CONTAINING GAS THROUGH SAID WELL BORE INTO SAID RESERVOIR SUCH THAT SAID SUBSTANCE CAN BE IMMEDIATELY CONTACTED BY SUBSEQUENTLY INJECTED OXYGEN-CONTAINING GAS TO INITIATE OXIDATION AND OXIDIZING SAID SUBSTANCE WITH OXYGEN-CONTAINING GAS TO PRODUCE HEAT SUFFICIENT TO IGNITE HYDROCARBONS PRESENT WITHIN SAID RESERVOIR. 